The present invention relates to a method and apparatus for treating electrically conductive fluid, that is fluid having some electroconductive capability. More particularly, the present invention relates to a method and apparatus for ionizing water having a high mineral content to prevent the precipitation of solids from the water which would tend to form a scale on the inner surface of piping through which the water flows, and to aid in the removal of a previously formed scale.
In systems using steel pipes, for example, through which water flows, a scale mainly consisting of ferric oxide is deposited on the inner surface of the pipes thereby reducing the inner diameter of the pipes resulting in a reduced flow rate and water pressure. The use of ionized water to remove such a scale is well known to those of ordinary skill in the art. When ionized water flows through piping having an oxide scale deposited on the inner surface thereof, the oxide scale is converted into a soft hydroxide (ferric hydroxide) which can be gradually removed.
U.S. Pat. No. 4,902,391 discloses a method and apparatus developed by the present inventor for ionizing, with great efficiency, fluids having a high dissolved solid content for the purpose of eliminating the problems caused by the deposition of substances such as ferric particles on the inner surface of fluid piping.
According to the method and apparatus disclosed in U.S. Pat. No. 4,902,391, two electrodes of electrically conductive materials having different electrochemical potentials, e.g. aluminum and carbon electrodes, are used to provide a voltaic cell structure which employs fluid to be treated as the electrolyte of the cell, whereby the fluid is ionized owing to the electric potential of the electrodes.
In the development research related to the method and apparatus disclosed in U.S. Pat. No. 4,902,391, it was found that reducing the electric current flow through the fluid between the electrodes and achieving a voltage only condition, or potential, provided the best performance. Such a condition was achieved when there was no electroconductive member, such as a resistor, connected between the electrodes, that is, when the electrodes were in what can be referred to as an "open circuit" condition.
Thus, in a unique embodiment featured in U.S. Pat. No. 4,902,391, the electroconductive connection between the electrodes was only established by the fluid to be treated extending therebetween, thereby providing a structure in which minimum current flow and maximum potential difference between the electrodes was expected.
In fact, the present inventor carried out tests, described below, to illustrate that when electric current flows through the fluid and between the electrodes is reduced, there is an improvement in the ability of the device to prevent the precipitation of solids (Ca, Mg and Si) dissolved in the fluid and thus prevent the formation of a scale, particularly a silica scale which is the most difficult type of scale to prevent.
Various apparatus were constructed in which there were both a direct electrical connection established between the electrodes, and in which electrical resistors were connected between the electrodes. The resistors used ranged from low values of resistance to very high values of resistance (several millions of ohms). In a series of tests conducted with the assemblies, it was observed that the precipitation of Ca, Mg and Si particles commenced very early when there was a direct electrical connection between the electrode members, i.e. maximum current flow. When the resistance between the electrodes was increased to successively reduce the electric current flow, it was observed that the precipitation of the Ca, Mg and Si particles became further and further delayed along with a corresponding reduction in the amount of precipitated material and hence a reduction in the formation of a crystalline scale.
As these tests were continued, and the values of resistance were increased to reduce the electric current flow, the formation of a Ca, Mg and Si precipitate ceased and only a colloidal suspension was observed. And, with an even further increase in resistance between the electrodes, even the colloidal suspension began to form more slowly and then only in water having a high degree of hardness and greater electroconductive capability. The above tests were conducted with standard tap water having an initial electroconductivity of about 200 .mu.S/cm and with additional samples of water having portions thereof evaporated to obtain test samples of increased total hardness and greater electroconductive capability.
Two basic effects therefore became apparent from an analysis of the above-described tests. First, as the resistance was increased between the electrodes, the precipitated material took on a more amorphous form. Secondly, with an increase in the resistance between the electrodes, a gradually increasing amount of colloidal suspension which did not readily participate was formed as well.
From such an analysis of the test results, it is postured that electric current flow through the fluid, as provided by a direct electrical connection between the electrodes or by a relatively small resistance, caused early precipitation of the dissolved solids (Ca, Mg, Si). It is also noted that precipitated material under such conditions was observed under a microscope as having a crystalline structure.
On the other hand, when there was relatively very little current flow and a condition of nearly voltage potential only was provided, the coalescence and crystallization of the dissolved solids did not occur and only a colloidal suspension of particles was formed due to the ionization of the fluid giving rise to electric charges of the same polarity (positive or negative) on the particles. In other words, the electric charges of the same polarity held the particles apart and prevented their coalescence and crystallization.
Although the above-described embodiment disclosed in U.S. Pat. No. 4,902,391, in which only the fluid to be treated was used to establish an electroconductive connection between the electrodes, was designed to achieve a voltage potential only condition, very minute currents were generated through the fluid and between the electrodes due to the changing electroconductivity of the fluid as it passed between the electrodes from entrance to exit. If the initial electroconductivity of the fluid to be treated is high, then even a greater amount of current is generated thereby reducing the effectiveness of the device to prevent the precipitate of dissolved solids and the formation of scale. Accordingly, in the device disclosed in U.S. Pat. No. 4,902,391, the efficiency and capability thereof to prevent the formation of a scale (Ca, Mg and Si) and to aid in the removal of a previously deposited scale in fluid containment systems commences to fall off at electroconductivity levels approaching 1,000 .mu.S/cm. Although this is highly satisfactory for normal water supply sources, it is unsatisfactory for many industrial applications which employ subterranean water often having a high dissolved solvent content level and electroconductivity levels in the order of 3,000 .mu.S/cm.
With the continuation of research for the further reduction of electric current flow, it became obvious that the spacing between the electrodes could be increased to provide an additional reduction of electric current flow. However, such a solution was limited by the physical restraints imposed by the systems in which the ionizing apparatus was to be employed. In addition, the systems also impose limitations on the size of the electrodes which could be employed. And, since the size of the electrodes corresponds to the area over which the fluid can be effectively treated in the system, then such physical restraints on the size of the electrodes and the spacing therebetween often renders impractical the solution of spacing the electrodes far enough apart to sufficiently reduce the electric current flow.